Projection objective

ABSTRACT

The invention relates to a projection objective which consists of at least seven lenses that are adjacent to air on both sides. The inventive projection objective meets the criteria of the following equations in its totality: u≧12.8°; 100 mm≦LEP≦400 mm; σRBa≧1°; σRBi≦−14°, whereby u is the aperture angle (2u-entire angle) on the illumination side; LEP is the distance from the entrance pupil (on the illumination side) to the object level (the position in the direction of projection from the reference point: object level corresponds to a positive value); σRBa is the angle inclination of the beam in relation to the optical axis in the object space between the object and the 1. lens surface of the objective, said beam limiting the bundle for the field edge (outer field point in the object) towards the outside (away from the optical axis, far from the axis) and σRBi is the angle inclination of the beam in relation to the optical axis in the object space between the object and the 1. lens surface of the objective, said beam limiting the bundle for the field edge (outer field point in the object) towards the inside (towards the optical axis, close to the axis). The angles σRBa and σRBi are positive when the corresponding beams intersect the optical axis in a point which is situated in the opposite direction of projection when seen from the object. Said angles are negative when the beams intersect the optical axis in a point which is situated in the direction of projection when seen from the object.

SCOPE OF THE APPLICATION

[0001] The invention's main scope of application is in movie projection, especially with 35 mm film.

CHARACTERISTICS OF ESTABLISHED TECHNICAL SOLUTIONS AND GOAL STATEMENT

[0002] The invention relates to a luminous projection objective. Known objectives of this type (DE-OS3833946) have been designed for the requirements with projections, whereby the focus is mostly on the grade of reproduction quality. Over many years this has led to a variety of modified Double Gauss objectives (DEOS 3633032, U.S. Pat. No. 4,704,011), which most of all sought to further reduce aberrations. Among other things, one result of this development is that in an advantageous design development, the diaphragm is preferably located in the larger space between the hollow inner surfaces of meniscus-shaped lenses, which is characteristic for Double Gauss objectives. However, this location, though advantageous for the correction of aberrations, exhibits significant disadvantages with projections, as the entrance pupil's resulting location on the lighting side is not adjusted in the best possible manner. Documents DE-OS 3029929 and DE-OS 3029916 point out the pupils' locations and their significance in relation to condenser adjustment in projections. The locations of entrance pupils, however, are not the only deciding factor in their best possible adjustment to lighting. Rather, the influence of solid angles above the lit object area on a partial luminous flux must be considered. These typical luminous flux diffusion characteristics require the adjustment of all object parameters relevant to lighting: location of an entrance pupil, opening and angles σRBa, as well as σRBi, restricting bundles. If this is not the case, such as with thus far known technical solutions, losses in the projected images' illumination intensity are the result.

PURPOSE OF THE INVENTION

[0003] The purpose of the invention is an objective, respectively a series of objectives, which on one hand guarantees the most effective use of luminous flux diffusion throughout an entire object area and on the other hand exhibits image quality, which is better or the same as the image quality of known technical solutions being used with technologically advantageous glasses.

DISCLOSURE OF THE INVENTION'S CHARACTERISTICS (SOLUTION AND ACHIEVED ADVANTAGES)

[0004] In accordance with the invention, this goal is accomplished with an objective according to the characteristics in claim 1. An objective according to the invention is characterized in that it maintains all effectivity parameters for adjustment to condenser systems in comparison to the aforementioned systems (DE-OS 3833946). Specifically, this indicates among other things an increase in the opening relationship from 1:2.4 to 1:1.9 and a reduction in vignetting of 61% to 73% for the most outward field point. This considerable expansion of the opening, axially as well as extra-axially, was achieved while maintaining image quality, including all image aberrations, when compared to the aforementioned systems.

[0005] The projection objective's design development according to the invention is already different from known solutions according to documents U.S. Pat. Nos. 2,701,982, 2,897,724 and 3,005,379 in that they are system examples with sealing devices. Also, reproduction quality is substantially worse with these objectives. Furthermore, neither the number of lenses nor the sequence of refractive power and lens shape match in the objectives of U.S. Pat. No. 2,701,982 and 2,897,724. Though the sequence of refractive power is identical to a system as per U.S. Pat. No. 3,005,379, the shape is not. Only the first and last lenses are the same as far as shape is concerned.

[0006] According to claim 1, an objective according to the invention satisfies the stated conditional equations, guaranteeing the most effective adjustment to the condenser systems. In order to illustrate the characteristics of this component of the invention, the luminous flux diffusion of the condenser systems employed in the projection of movies must be explained in further detail. Luminous flux diffusion means a partial luminous flux' dependence on the solid angle for a small area element at object level. A solid angle's zero axis runs through the field point in view and is parallel to the lighting system's axis. The characteristics of spatial luminous flux diffusion following in direction of projection behind this small area element contain all the properties of a condenser system relevant to lumen technology. The luminous flux' diffusion depends on the object area and exhibits diffusion at the lighting system's axis, which is virtually radial in symmetry. With smaller solid angles in the direction of the axis, the luminous flux is zero due to constructive necessity, it increases at a steep rise up to its peak value, and then flatly decreases outwardly. This diffusion changes outward via the object area. Radial symmetry is thereby lost, and the maximum of luminous flux diffusion moves in the direction in which the entrance pupil's center appears, when seen from the lit field point. In that part of the bundle of rays, mirrored at the solid angle's axis and located toward the maximum of luminous flux diffusion, the luminous flux is reduced significantly. Its maximum value only amounts to a fraction in comparison to the other portion of the bundle. Energetic diffusion therefore becomes highly asymmetrical.

[0007] For example, if objective aperture u=14.7° (equivalent to a diaphragm value of k=1.9 at a fictitious projection distance of infinite) in the reproduction of an object area's border sections and is therefore well adjusted to the lighting aperture, but the location of the entrance pupil LEP is <100 mm, the result will be that an essential portion of the exterior entrance pupil area, which is located opposite the viewed field point in relation to the optical axis, is not at all involved in the reproduction; and on the other hand essential parts of luminous flux diffusion in the exterior entrance pupil area, located on the same side as the viewed field point in relation to the optical axis, are clipped, even with only minor vignetting. Furthermore, an aperture of only u=11.8° (equivalent to k=2.4) will lead to yet larger losses of light, as portions of the luminous flux maximum's environment are clipped. This effect is even greater with increased vignetting.

[0008] However, if the location of the entrance pupil is LEP>400 mm with an aperture of u=14.7°, significant parts of the luminous flux' diffusion are clipped by exterior entrance pupil areas, located opposite the viewed field point in relation to the optical axis, and the luminous flux has negligible values in the exterior entrance pupil areas, located on the same side as the field point viewed in relation to the optical axis. One must further observe that an entrance pupil's location of LEP>400 mm results in larger lens diameters on the object's side and impedes the correction of aberrations.

[0009] This is the case with the mentioned systems (DE-OS 3833946), which are already known.

[0010] All these significant disadvantages have been removed with an objective according to the invention. An aperture of u=14.7° (k=1.9) captures the energetically essential part of a luminous flux on the axis. In field range, the location of entrance pupil LEP and angles σRBa and σRBi, restricting the bundles, ensures that the objective captures the luminous flux infiltrating each area element in the field in the best possible manner and that the luminous flux is therefore utilized for the projection image's illumination intensity. At the same time it is thus prevented that areas of the pupil are infiltrated by energetically non-essential bundles of light, which do not reasonably play a significant role in the composition, but unnecessarily impede the balance of reproduction aberration compensation and result altogether in worse reproduction quality.

[0011] One essential performance increase in optical reproductions with technologically advantageous glasses could only be achieved with a modified sequence of positive and negative refraction power, while largely maintaining a Double Gauss structure favoring aberrations, whereby it was necessary to allow for an increase in the lenses' individual aberrations.

[0012] To produce a focal distance series in steps, necessary for the adjustment of projection conditions, using the same types of glass for equivalent lenses poses a decisive technological advantage. Furthermore, only technologically advantageous, i.e. process and cost effective glasses are used.

[0013] One preferred application of a projection objective according to the invention is the use of the objective alone, i.e. without additional components. It is entirely usual within the context of the invention to combine separate optical components with the projection objective. These components may, for example, be objective attachments or objective supplements, especially attachments for focal length variation and anamorphic attachments for panorama wide screen projection. It is conceivable to integrate attachments mechanically.

DESIGN DEVELOPMENT EXAMPLES

[0014] Preliminary Remark:

[0015] For practical reasons, the sectional views, flux progressions and evaluation of reproduction quality in the following illustrations refer to a reversed position opposite the projection objective's position of use (reproduction from enlarged to shrunk side.) The entrance's intersection width s=infinite. Therefore the original object is inevitably turned toward the image and reversed. This reversal is referenced colloquially. An exception to this is pupil reproduction (orientation in position of use). This should be noted in the following explanations.

[0016] The following illustrations exhibit the luminous projection objective with a curved image area according to claim 3:

[0017] 1.1a System's sectional view with numbered lenses and flux progression on the meridional level for the reproduction of different object points. The diaphragm is located between lenses 2 and 3.

[0018] 1.1b System's sectional view with flux progression on the meridional level for the reproduction of the most outward object (the object area's diagonal) and characteristic angles σRBa and σRBi with values: σRBa=4.4° and σRBi=17.1° for an entrance pupil location LEP=166 mm. Therefore the pupil's size and angular location relative to the solid angle axis for the reproduction of axial and extra-axial points up to the margin are optimized for the condenser systems' luminous flux diffusion. In addition, the angular values of σRBa and σRBi ensure that energetically important areas of luminous flux diffusion, which are field-dependent, are captured by the pupil, yet they also ensure that unnecessary areas of luminous flux diffusion are not positioned in the pupil's area, as they are energetically insignificant. This introduction of vignetting, which is oriented and guided by the actual relationship of the condenser systems, also prevents pupil areas from negatively impacting reproduction quality in the corrective compensation during optimization of reproduction quality, as they, in any case, play only an insignificant role in the entire reproduction.

[0019] 1.2 Course of vignetting for the 3 main colors λ(d)=587.6 nm, λ(C)=656.3 nm and λ(F)=486.1 nm with weightings λ(d)=1, λ(C)=λ(F)=0.5, depending on half image angle w(wmax=13.2°). Minimal vignetting value amounts to 74% and is essentially also determined by angle σRBa. A comparison to the aforementioned solutions (DE-OS 3833946) clearly shows significantly lower vignetting of approximately 12%, less abruptly and progressively decreasing curve progression and also a considerably larger opening.

[0020] 1.3 Meridional (tan) and sagittal (sag.) modulation transfer function MTF for the 3 main colors λ(d)=587.6 nm, λ(C)=656.3 nm and λ(F)=486.1 nm with weightings Λ(d)=1, λ(C)=λ(F)=0.5, depending on half picture angle w (wmax=13.2°) for spatial frequencies 60 LP/mm, 30 LP/mm and 15 LP/mm. A comparison to the aforementioned solutions (DE-OS 3833946) shows much better and balanced reproduction quality throughout the entire image area when being fully open. As it were, contrast remains constant throughout the entire image area for 30 LP/mm at a high absolute value of approximately 80%, while the aforementioned solutions exhibit a contrast decrease of 20% with a lesser diaphragm value of k=2.0 and an absolute contrast value declining to 60%.

[0021] 1.4 Spherical aberrations Δy′ and Δx′ for the 3 main colors in the meridional (T) and sagittal (S) sections, depending on entrance pupil radius pEP for half picture angle w=0, w=0.25×wmax, w=0.5×wmax, w=0.75×wmax as parameter with w=wmax=13.2°. These curves show the corrective behavior, depending on the pupil and field coordinates for these 3 wavelengths. They confirm the excellent reproduction quality throughout the entire image area, as demonstrated already by the modulation transfer function's curve progression, and provide deeper insight into the system's corrective behavior. They further illustrate excellent axial and lateral color correction.

[0022] 1.5a to 1.5c Astigmatism for the 3 main colors depending on the picture's angle. Maximum astigmatic difference is 0.03 mm. This is the maximum deviation between the meridional and sagittal curve progressions, i.e. the deviation from the curved image shell. It is a very small value, which in any case appears only in a certain zone of the object field and again becomes zero at image margin.

[0023] 1.6 Distortion depending on the picture angle for the mid-primary color. Distortion achieves a maximum deviation of 0.7% at image margin.

[0024] Therefore the two aberrations according to illustrations 1.5a to 1.5c and 1.6 are also better, respectively the same, compared to the aforementioned solutions (DE-OS 3833946).

[0025] Illustrations 2.1 to 2.6 illustrate the luminous projection objective with a level object field according to claim 4 in the same manner as was the case in illustrations 1.1 to 1.6. The illustrations show:

[0026] 2.1a System's section with numbered lenses and flux progression on the meridional level for the reproduction of various object points. The diaphragm is located between lenses 2 and 3.

[0027] 2.1b System's section with flux progression on the meridional level for the reproduction of the most outward object point (object field's diagonal) and characteristic angles σRBa and σRBi with values: σRBa=5.3° and σRBi=16.2° for an entrance pupil location LEP=199 mm.

[0028] 2.2 is equivalent to illustration 1.2. Minimum vignetting value is 74%.

[0029] 2.3 is equivalent to illustration 1.3. Contrast remains practically constant throughout the entire image area for 30 LP/mm with a high absolute value of approximately 78%.

[0030] 2.4 is equivalent to illustration 1.4.

[0031] 2.5a to 2.5c are equivalent to illustrations 1.5a to 1.5c. In this case, however, the curves refer to a level image area.

[0032] 2.6 is equivalent to illustration 1.6.

[0033] The curve progressions in illustrations 2.2 to 2.6, all of which contain an evaluation of reproduction quality, show that the same grade of reproduction is possible even with level image areas. 

1. A projection objective consisting of seven lenses bordering to space on both sides, characterized by the following conditional equations, which must be met in their entirety: u≧12.8°, 100 mm≦LEP≦400 mm, σRBa≧1°, σRBi≧−14°, whereby u is the aperture angle (2u-entire angle) on the lighting side, LEP is the distance of the entrance pupil (on the lighting side) to object level (the location in direction of projection from reference point object level is a positive number), σRBa is the ray's angular slope opposite the optical axis in the object space between the object and the objective's 1^(st) lens area, which limits the bundle for the field margin (object's outer field point) outwardly (away from the optical axis, distant from the axis) and σRBi is the ray's angular slope opposite the optical axis in the object space between the object and the objective's 1^(st) lens area, which limits the bundle for the field margin (object's outer field point) inwardly (toward the optical axis, near the axis), as well as that angles σRBa and σRBi are positive, if the respective rays intersect the optical axis at a location, which, when seen from the object, is in the opposite direction to projection and negative, if intersecting the optical axis at a location, which, when seen from the object, is in direction of projection, with the following lens locations in sequence from image (enlarged side) to object (shrunk and lighting side): a first biconvex lens (1), a second negative lens (2), with concave surface at image side, a third positive lens (3), with convex surface at image side, a fourth negative lens (4), with concave surface on object side, a fifth negative lens (5), with concave surface at image side, a sixth positive lens (6), with convex surface on object side, and a seventh biconvex lens (7).
 2. A projection objective according to claim 1, characterized by the following data for lenses (1 to 7): TABLE 1 Area Thickness and Refractive Abbe Lens No. No. Radius Distance Index Value Value j i ri/f′ di/f′ nd vd 1 0.89 < ri/f′ < 1.37 — 1.0000 — 1 2 −1.34 < ri/f′ < −0.93 0.10 < di/f′ < 0.16 >1.60 <50 3 −0.96 < ri/f′ < −0.79 0.005 < di/f′ < 0.02 1.0000 — 2 4 −∞ ≦ ri/f′ < −2.00 0.04 < di/f′ < 0.08 >1.59 <50 5 0.43 < ri/f′ < 0.55 0.001 < di/f′ < 0.004 1.0000 — 3 6 −4.03 < ri/f′ < −1.09 0.11 < di/f′ < 0.20 >1.60 >45 7 −∞ ≦ ri/f′ < −2.00 0.001 < di/f′ < 0.03 1.0000 — 8.0 < ri/f′ ≦ ∞ 4 8 0.30 < ri/f′ < 0.38 0.03 < di/f′ < 0.12 >1.59 <40 9 −0.35 < ri/f′ < −0.27 0.16 < di/f′ < 0.26 1.0000 — 5 10 0.98 < ri/f′ < 3.73 0.03 < di/f′ < 0.10 >1.59 <40 11 −3.15 < ri/f′ < −1.82 0.01 < di/f′ < 0.08 1.0000 — 6 12 −5.10 < ri/f′ < −0.40 0.08 < di/f′ < 0.18 >1.60 >45 13 0.85 < ri/f′ < 1.33 0.001 < di/f′0.004 1.0000 — 7 14 −1.28 < ri/f′ < −0.65 0.09 < di/f′ < 0.27 >1.60 >45


3. A projection objective according to claim 1 or 2, characterized by the following data for lenses (1 to 7): TABLE 2 Lens Area Thickness and Refractive No. No. Radius Distance Index Value Abbe Value j i ri/f′ di/f′ nd vd 1 60.583 — 1.0000 — 1 2 −75.475 6.215 1.68893 31.06 3 −55.307 0.800 1.0000 — 2 4 −656.958 2.765 1.71736 29.50 5 28.998 0.200 1.0000 — 3 6 −120.159 6.912 1.64000 60.05 7 −608.478 0.200 1.0000 — 4 8 19.868 6.617 1.67270 32.09 9 −17.785 12.062 1.0000 — 5 10 149.747 2.556 1.71736 29.50 11 −184.302 1.000 1.0000 — 6 12 −25.205 6.195 1.70000 48.06 13 64.146 0.100 1.0000 — 7 14 −47.864 9.399 1.70000 48.06


4. A projection objective according to claim 1 or 2, characterized by the following data for lenses (1 to 7): TABLE 3 Lens Area Thickness and Refractive No. No. Radius Distance Index Value Abbe Value j i ri/f′ di/f′ nd vd 1 58.672 — 1.0000 — 1 2 −69.023 6.436 1.68893 31.06 3 −52.519 0.800 1.0000 — 2 4 −2339.829 2.892 1.71736 29.50 5 25.774 0.200 1.0000 — 3 6 −140.168 7.955 1.64000 60.05 7 738.395 0.200 1.0000 — 4 8 18.251 4.000 1.67270 32.09 9 −16.267 12.868 1.0000 — 5 10 112.132 3.000 1.71736 29.50 11 −188.336 1.300 1.0000 — 6 12 −24.858 5.849 1.70000 48.06 13 70.379 0.100 1.0000 — 7 14 −40.309 8.858 1.70000 48.06 